Engineering insight, dogged determination and a dash of serendipity have made the lowly inkjet imaging device the king of computer printers

IN THE annals of computing, nothing has caused as much disappointment as putting ideas on paper. For decades, printing computer files was a thankless task for users who were seeking to reproduce precisely what they saw on the computer screen. Then along came the inkjet printer that sprayed tiny dots of ink on to the paperâ€”and so started a revolution in the printing of high-quality images that was more important than anything since photogravure.

Thermal inkjets, first commercialised by Hewlett-Packard and Canon in the 1980s, began as slow, messy machines that were no match for the costlier laser printers that had just been introduced. But eventually, the scrappy little inkjet printers got better and better. Today, an inkjet printer costing less than $50 will spit out crisp colour pictures, sharp text and brilliant graphics as good as any laser printer costing 30-40 times more. No wonder inkjets outsell laser models twelvefold. Inkjet cartridges alone now account for $19 billion of annual sales, according to Lyra Research, a consultancy in Newtonville, Massachusetts.

For all its originality, the idea behind the inkjet is far from new. As long ago as 1867, William Thomson (later known as Lord Kelvin) was granted a patent for â€œReceiving or Recording Instruments for Electrical Telegraphersâ€ which used electrostatic forces to control the release of ink drops on to paper. In 1951, Siemens produced the first continuous inkjet printer. And throughout the 1960s, other manufacturers unveiled improvements on the same ideaâ€”all with little success. Inkjets proved expensive, messy and unreliable, with pumps, bladders and other moving parts that simply could not deliver an affordable machine capable of producing high-quality prints.

The modern inkjet solved these problems with a self-contained print head, complete with inkwell, spraying mechanism and nozzles that could be controlled accurately. Throughout the 1970s, research into the technology focused onpiezoelectric methods. These use special crystals that vibrate when charged to squeeze out controlled amounts of ink. The most compelling innovation, however, came when engineers turned to heat instead of vibration.

The thermal inkjet printer was invented not once, but twice. The idea was conceived simultaneously, and unbeknown to one another, by two competing teams on either side of the Pacific. In Japan, Ichiro Endo, an engineer at Canon, noticed ink squirting from the neck of a syringe when a hot soldering iron touched it. Thousands of miles away at Hewlett-Packard’s laboratories in Silicon Valley, a researcher called John Vaught dreamed up his version of the thermal inkjet by borrowing from the mechanism of the coffee percolator.

Hewlett-Packard’s efforts began on Christmas eve, 1978. Together with David Donald and a group of other engineers, Mr Vaught began idly to discuss concepts for an ideal printer. The team had just delivered the engine for HP’s first laser printer and was working on a gravure printer for the commercial-publishing world. Despite this, the team wanted moreâ€”especially colour, speed and, most important of all, low cost.

That was a tough combination. At the time, printers fell into two categories: impact and non-impact. Typewriters aside, the most common impact printers were dot-matrix devices, which used an array of pins to strike an ink ribbon to form characters or other images. Non-impact printers, by contrast, offered more hope. By not touching the paper when making an image, they promised to be more accurate and efficient.

Although far from mature, no fewer than five non-impact technologies were vying for success. There were inkjets that sprayed microscopic dots of ink through hundreds of tiny nozzles on to paper; laser printers that used a laser beam and the xerography process to affix toner to paper; solid-ink printers that employed a similar technique to melt sticks of a coloured wax-like ink on to paper; dye-sublimation printers that relied on long rolls of film, heated to embed dyes into special paper; and thermal autochrome printers that applied heat to a special type of paper already impregnated with dyes to produce colour prints.

In 1978, the inkjet concept caught Mr Vaught’s imagination, because it promised to yield a simple, low-cost and high-performance printer. Despite its shortcomings, the technology was considered to have far greater potential for improvement than its rivals. That afternoon, before departing for the Christmas holiday, Mr Vaught and his colleagues concluded that the ideal printer was an inkjet machine that could deliver 200 dots per inch and be capable of printing in full colour. Over the holiday, Mr Vaught set the ground rules: the new type of printer would have an array of ink nozzles spaced a two-hundredth of an inch apart and be able to feed ink fast enough to print one page per second.

Returning to the laboratory after Christmas, Mr Vaught focused on building a solid-state print head that would experience less wear and no clogging, but still be able to spit ink out fast enough for the job. As he watched a coffee percolator, he realised the answer was to use the ink itself to shoot dots on to paper.

â€œThe race to develop the inkjet printer had a profound cultural impact on both companies.â€

To do so, he tried using a pair of electrodes with the ink between them acting as a resistor. The idea was to get the heat to vaporise a small portion of ink very near a nozzle, causing it to spit out a droplet. Unfortunately, the ink did not have high enough resistivity to create the necessary heat. Worse, the process electrolised some water in the ink into hydrogen and oxygen, which interfered with the operation.

Mr Vaught then tried harnessing the hydrogen and oxygen to produce a micro-explosion capable of firing the ink out of the nozzle. A small spark could be induced across the electrodes to ignite the hydrogen bubbles and spit out a drop of ink, but the process was nowhere near fast enough. In a third attempt, Hewlett-Packard engineers opted to put all the energy into the spark itself, in order to boil a bubble of ink. That succeeded, but the electrodes quickly deteriorated.

The breakthrough came when Mr Vaught and his colleagues seized on thin-film resistors. These were found to be able to produce enough heat to boil a bubble of ink and spit a dot out rapidly with a high degree of control. The resistors were mounted inside small tubes that were etched with grooves to create the nozzles, and switched on and off rapidly to spit out microscopic dots of ink. Within three months, the Hewlett-Packard team had concocted a workable version of a thermal inkjet mechanism.

Surprisingly, for all their engineering insight, the team could not explain exactly why their printer worked. And although it worked well, and was patentable without an underlying theory, Hewlett-Packard’s middle managers were reluctant to invest in the idea. Some top HP managers dismissed the invention altogether. As it turned out, the physics of Mr Vaught’s processâ€”known as â€œphreatic reactionâ€â€”would not be understood fully for another year.

But Mr Vaught doggedly pursued his interest in the inkjet printer. He demonstrated his work to anybody who took an interest, eventually catching the eye of, among others, Larry La Barre, an HP old-timer who was able to persuade the company’s management to take the technology more seriously. Thereafter, Hewlett-Packard started showeringR&D funds on inkjet technology, and the programme became a critical part of its future.

Canon ball

Meanwhile, Mr Endo had already started work on a broadly similar effort. Canon’s goal was to create better xerographic technology, inkjets being just one of several options. Back in 1977, Mr Endo and his team focused on fabricating a piezoelectric system that could send electronic pulses through a nozzle, creating enough force to shoot ink from the chamber. But when a researcher accidentally touched the tip of an ink-filled syringe with a soldering iron, the squirt of ink changed the course of Canon’s research and subsequent fortunes.

Within days, Mr Endo and his team used the discovery to build a simple inkjet printer that would come to be known as the Bubblejet. The main difference between this and HP’s invention lay in how the ink was fired: Canon’s shot ink out sideways, while HP’s print heads released their ink from the top.

Two years later, Hewlett-Packard found out about Canon’s work. The patents for many of the key inventions in both research efforts had been filed within months of one another. The result was a relationship between Canon and HP that continues to this day. Hewlett-Packard has borrowed some of Canon’s designs for extending the life of the print head, while Canon has borrowed from HP’s ideas for print-head configuration. Despite brief disagreements over rights to the technology, Hewlett-Packard insists that the co-operation has developed into a healthy competitive relationship between the two companies, and moved the state of the art further than it would otherwise have gone.

Following the two initial inventions, the development of inkjet technology became a multidisciplinary effort. New quick-drying and light-fast inks had to be developed. Improvements in the print jets continued apace. Better mechanisms for feeding the paper, and new software to improve image quality, were added. To raise speed still further, engineers on both sides developed faster motors and lightened their print-head mechanisms, while increasing the number of nozzles on their heads. More features were added to the inkjets, and soon hybrids of the technology that turned printers into fax machines and copiers emerged. Today, multifunction machines are the fastest-growing bit of the printer market.

The race to develop the inkjet printer had a profound cultural impact on both companies. For instance, disposable print heads, developed in 1984, are said to have caused no end of grief at Hewlett-Packard. The very thought of disposing of the little plastic units that contained the printers’ intellectual property was anathema to some of HP’s executives.

Other competitors entered the market with designs of their own. Epson introduced its inkjet line based on piezoelectric technology first investigated in the 1970s. Lexmark and Agfa also jumped in, focusing on specialised applications such as digital photography and graphic arts. But for all the interest, the growth of the inkjet market got off to a poor start. Compared with Hewlett-Packard’s Laserjets, which were seeing healthy sales growth, the inkjet market appeared to languish after the company created its first Deskjet range in the late 1980s. At one point in the mid-1990s, HP even pondered pulling the plug.

Colour to the rescue

The widespread use of colour in computing during the mid-1990s changed everything. Just as Mr Vaught had planned, adding colour capability to inkjets was the next logical step. Print heads with complementary colours of magenta, cyan and yellow were added to black ink, enabling printers to create a full range of colours. More specialised photo printers have also added various shades of the primary colours to produce ever more faithful reproductions. â€œWe essentially took all the work of craftsmen in a printshop and put it in algorithms,â€ says John Meyer, a director at HP’s laboratories. As computers became ever faster, those algorithms allowed prints to become sharper and ever more vibrant.

Today, the inkjet is no longer a cheap substitute for a laser printer, but a graphics machine in its own right. The average print head now contains more than 300 nozzles and is capable of producing images with a resolution of at least 1,200 by 1,200 dots per inchâ€”more than the eye can resolve. The average machine can now fire ink at a blinding 14,000 dots per second, depositing more than 1m drops of ink on a square inch of paper. Most of the development work is now going into creating durable, light-fast inks to prevent pictures from fading. Meanwhile, new software is helping to produce clearer pictures by controlling the printing pixel by pixel.

Ultimately, the development of the inkjet printer underscores how lateral thinking can yield remarkably simple solutions to complex problems. Both Mr Endo and Mr Vaught, who have shared numerous industry awards in recognition of their accomplishments, displayed dogged determination and belief in their inventions, despite much internal resistance. But in doing so, they revolutionised the computer business and brought colour to people’s lives.